1. Field of the Invention
The present invention relates to an auto-guided vehicle (AGV) that transfers a substrate for forming a semiconductor device in a clean room. The present invention also relates to a production system and a production management method for a semiconductor device, for managing a production line that uses the AGV for a semiconductor device
2. Description of the Related Art
In a production line for a semiconductor device, a cleanliness level required for a clean room is varied depending on a degree of integration. In general, it is considered that a dust with a grain size that is equivalent to one tenth of a design rule or more has an influence on characteristics of a product, and a higher cleanliness level is required for a clean room with a higher degree of integration.
In order to obtain the higher cleanliness level, an AGV that automatically transfers a substrate between manufacturing systems in a clean room. With the automatic transfer by the AGV, a human body that is most a source of a dust can be kept as far away from the clean room as possible. Therefore, it is possible to the higher cleanliness level and to improve yield of a production. To the transferred substrate, a process for an object is performed in each manufacturing system.
In particular, in a production system called a job shop system, in which manufacturing systems of the same kind in a factory are put together into a group of equipments in a plant and a substrate that is an object to be processed is moved between the groups of equipments, the automatic transfer with the AGV is quite useful. In the case of a large-sized plant, not only a cleanliness level in a clean room can be improved but also an advantage of eliminating a loss of time due to waiting for an operator can also be obtained.
In general, the AGV performs transfer with containing one or plural carriers in which a substrate is stored. In a space (a containing portion) for containing the carrier in the AGV, air filtered through a filter provided with the AGV is introduced to keep a cleanliness level in the containing portion thereby (for example, Reference 1: Japanese Patent Laid-Open 11-322068).
By the way, a thin film transistor that is one of active devices, provided in a semiconductor device, is completed through various manufacturing processes, typically, which mainly include forming a base film for preventing penetration of an impurity in a substrate into a semiconductor film, forming and crystallizing the semiconductor film, patterning of the semiconductor film, forming a gate insulating film, forming a source/drain region, and forming a gate electrode.
For the process of forming the source/drain region in the processes above, doping with an impurity for imparting conductivity is performed to the semiconductor film. The doping includes ion implantation and thermal diffusion. In the case of imparting an n-type, an element that functions as a donor (an element of Group 15 such as P, As, or Sb, or an element of Group 16 such as S, Te, or Se) is used as a dopant to perform doping whereas an element that functions as an accepter (an element of Group 13 such as B, Al, Ga, or In, or an element of Group 12 such as Zn) is used as a dopant to perform doping in the case of imparting a p-type.
The dopant or a reaction product that adheres to the substrate in doping, however, is released into the atmosphere. Although an element as the impurity is necessary for forming the source/drain region, the impurity is a contaminant that becomes a cause of chemical contamination against the substrate in the process in a different manufacturing process, and it has an adverse affect on characteristics of the semiconductor device that the substrate is contaminated by the element.
For example, characteristics of a semiconductor device represented by a device such as a TFT are fluctuated, or in deposition with CVD, fluctuation in deposition rate is generated due to contamination of a surface on which a film is formed.
Since the substrate after doping is transferred with the AGV to a manufacturing system for the next process, there is the possibility that the atmosphere is contaminated by the impurity in a transfer route with the AGV as shown in Reference 1, which takes in once and exhausts air in a clean room in order to keep the substrate inside clean.
In addition, there is also concern about a harmful influence on a body of an operator working in the clean room due to diffusion of the impurity in the clean room.